Work extraction from downhole progressive cavity devices

ABSTRACT

A progressive cavity device and method of use are provided, the progressive cavity device comprising a hollow stator having a rotor shaft positioned therein. The rotor shaft is provided with rotating motion drive connections at both ends thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on and claims priority to GBApplication No. 0722445.4, filed 15 Nov. 2007; and International PatentApplication No. PCT/EP2008/009607, filed 6 Nov. 2008. The entirecontents of each are herein incorporated by reference.

TECHNICAL FIELD

This invention relates to techniques for extracting work fromprogressive cavity devices such as pumps (PCPs) and motors (PDMs). Inparticular the invention relates to such techniques for use withdownhole devices such as are used in wells in the oil and gas industry.

BACKGROUND ART

PCPs and PDMs comprise a hollow cylindrical stator with an elongaterotor positioned therein. The stator has helical lobes formed on itsinner surface, typically formed from some elastomeric material. Therotor has helical lobes formed on its outer surface. As is explainedbelow, the number of lobes and their helical pitch are different for therotor and stator of any pump or motor. The term ‘progressive cavitydevice’ is used here to mean any such device, whether configured as apump or as a motor. Progressive cavity devices are used in oilfieldapplications in two major segments: artificial lift and drilling. Theyhave shown a high life if designed and dimensioned properly, and havedemonstrated acceptable tolerance to finer solids (such as LCM duringdrilling and sand during production).

In both cases, the rotor and stator axes of a progressive cavity deviceare eccentric to each other, leading to a rotation of the rotor insidethe stator with a simultaneous nutation of the rotor centreline to thestator centreline. In the case of artificial lift, an electric motordrives the rotor through a eccentric universal joint to allow for theeccentricity of the rotor to the centre. In the case of drilling motors,the flow of drilling fluid through the device forces the rotor to rotateinside the stator, leading to a rotation of the drillbit through adouble universal joint system or a flexible drive shaft. Theconfiguration of the rotor/stator lobes is one-off (e.g. 1:2, 3:4, 7:8)and this ratio can be used to calculate the nutation speed of the rotoraround the centreline of the stator given the rotation speed of therotor on itself. The nutation rotation direction is opposite to that ofthe rotor rotation.

DISCLOSURE OF INVENTION

A first aspect of the invention provides a progressive cavity devicecomprising a hollow stator having a rotor shaft positioned therein,wherein the rotor shaft is provided with rotating motion driveconnections at both ends thereof.

The drive connections can be for driving the rotor shaft or forextracting drive from rotation of the rotor shaft. Preferably, at leastone of the drive connections operates at a speed that is different tothe rotation speed of the shaft.

The drive connections can couple to the rotation of the shaft. Suchdrive connections preferably comprise a shaft connecting two universaljoints, or a flexible shaft. Alternatively, the drive connections cancouple to the nutation of the shaft. Such drive connections can includea non-nutating connection that imposes a nutation speed on the shaft.Such a drive connection can comprise a disc mounted for rotation on afurther shaft, the rotor shaft being connected eccentrically to thedisc. Nutating connections can include, for example, a planetary gearsystem, the rotor shaft being connected to a planet gear.

The device can be configured to act as a motor or as a pump. Whenconfigured as a motor, the rotor is driven by pumping fluid through thestator, and a rotating drive connection is taken from both ends of thestator to power other devices. In a preferred embodiment, the drive atone end is used to rotate a drill bit. The drive at the other end can beused to power a crushing device or an electricity generating device.

When configured as a pump, the rotor is driven by a drive connectionfrom a motor at one end and a rotating drive connection is taken fromthe other end of the rotor to power other devices. Examples of preferreddevices to be powered via the rotating drive connection include fluidair mixers, crushing devices, reaming or drilling devices and fluidmixing/shearing devices.

This invention provides methods of tapping to and extracting rotation atboth ends of a progressive cavity device rotor. This rotation can beextracted at various rates and used to perform simultaneous operationswith the use of only one pump or motor. Even when one end of the pump iswhat drives the rotor to create a fluid circulation, the other end canbe used to perform additional work, without the need for anotherhydraulic or electric motor being added. Potential applications exist invarious oilfield segments.

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

FIGS. 1 and 2 show axial and radial sections of rotor/statorcombinations for progressive cavity devices;

FIG. 3 shows one embodiment of a non-nutating drive connection;

FIG. 4 shows another embodiment of a non-nutating drive connection; and

FIGS. 5 and 6 show embodiments of progressive cavity devices with driveconnections at both ends of the rotor.

BEST MODE FOR CARRYING OUT THE INVENTION

This invention provides techniques for tapping to and extractingrotation of both ends of a progressive cavity device rotor. For example,this rotation can be used for a cuttings crusher at the entrance of thedevice, or for a gas/fluid agitator at the end of a downhole pump. Thisinvention describes how different output speeds can be utilized invarious oilfield applications.

The power section of a downhole motor converts hydraulic energy from thedrilling fluid into mechanical energy to turn the bit. Using the reverseMoineau pump principle, the positive displacement motors operate byusing the surface pumps to force the drilling fluid between a helicalshaft, and a sealing sheath. The helical shaft is rotated by the fluidand is called the “rotor”, while the sheath is fixed and called the“stator.” The stator is connected to the rest of the drill-string (or aCoiled Tubing) via the top sub. Thus the inertia of the drill stringcounters the torque created by the operation of the motor. The statorwill only rotate when the drill string is rotated when driven from thesurface.

A relatively known and constant amount of rotation is required to pass afixed volume of fluid through the system, so the motor rotation, orrevolutions per minute (rpm), is proportional to the flow rate. A smallpart of the flow ‘bypasses’ doing rotary work as it leaks through therotor and stator contact line from a high-pressure cavity to an adjacentlow-pressure cavity.

Both rotor and stator have matching helical profiles, but the rotor hasone less spiral (or lobe) than the stator. FIGS. 1 and 2 show axial andradial sections of rotor/stator combinations. In FIG. 1, the rotor 10has a single lobe and the stator 12 has two lobes 14 (ratio 1:2). InFIG. 2, the rotor 16 has five lobes 18 and the stator 20 has six lobes22 (ratio 5:6). The power section of such a downhole motor is designatedby the ratio of its rotor/stator lobes. For example, a 4:5 power sectionhas four lobes in the rotor and five in the stator. Motors such as thePowerPak range of motors from Schlumberger are available in 1:2, 2:3,3:4, 4:5, 5:6, and 7:8 lobe configurations. The ratio of therotor/stator helical pitch is the same as the ratio of the rotor/statorlobes. For example, the stator pitch of a current commercial 5:6 lobemotor is 52.70 in, and the pitch of its rotor is (⅚)×52.70 in, or 43.92in.

In an assembled power section, the rotor and stator form a continuousseal at their contact points, producing cavities independent from eachother. As fluid (water, mud, or air) is forced through these progressivecavities, it causes the rotor to move around inside the stator. Themovement is the combination of rotation and nutation. When completing arevolution, the rotor nutates once for each of the rotor lobes.Therefore, nutation creates mechanical stresses on the motor at a muchhigher rate than the rotation itself, and becomes a limiting factor inmany cases. As an example, a motor with 7:8 rotor/stator lobeconfiguration rotating at 100 rpm has a nutation speed of 700cycles/minute.

In the case of an artificial lift pump, an electric motor is usuallysituated below the PCP pump and is driven via electrical cables runningfrom the surface.

Finally, in the case of a circulation pump in a wireline powered andconveyed drilling machine, an electric motor is placed above the PC pumpand drives it to create a fluid circulation to carry the cuttings. Thissame pump can also be used in to create a vacuum in low bottomholepressure reservoirs for sand and debris cleanout operations.

There are a number of ways in which the concept of this invention can beimplemented. In a conventional drive connection, the drive input oroutput connects to the rotor shaft axis such that one rotation of theshaft equates to one rotation at the drive connection. In one embodimentof the invention, instead of connecting to the rotor centre to extractor create the rotation, the connection can be via a non-nutating driveas shown in FIG. 3 that rotates (or dictates) the rotor *nutation*speed. In this embodiment, the end of the rotor shaft 40 projects fromthe stator which comprises a metal housing 42 having an elastomericinsert defining the lobe structure 44 (the example shown here is a 1:2system for simplicity, other ratios are equally applicable). Thenon-nutating drive comprises a nutation disc 46 fixed to the end of ashaft 48 which is itself mounted in bearings 50 for rotation. The end ofthe rotor shaft 40 connects to the nutation disc 46 by means of arotation bearing 52 which is offset from the disc centre. In use, wherethe rotor is being driven by fluid flow or a motor attached to the otherend of the rotor (not shown), the rotor shaft 40 is driven to rotateabout its axis in direction ω_(R) whereas the nutation at the end of therotor 40 is coupled via the disc 46 such that the shaft 48 rotates inthe opposite, nutation direction ω_(N). Alternatively, the shaft 48 isthe one that could be driven by a motor, the non-nutating connectionbeing used to provide a drive input to the rotor, typically when actingin a pump configuration.

Using the embodiment of FIG. 3, a faster spinning (and therefore moreefficient) electrical motor can be used to rotate a pump at a lower rpm.In the case of a downhole motor, the rotation of the bit can be at thefaster nutation rate, and allows use of faster-turning bits without thenecessity for a high rotor rotation rate. Typical rotation rates fordrilling bits are in 100-300 rpm. Thus, when connecting directly to therotor shaft rotation for drive, a 200-600 rpm nutation of the rotor inthe stator (of a 1:2 motor) must be accommodated, increasing the fatiguestresses on the stator elastomer. If the nutation is used as the drivevia the non-nutating connection, then for a 300 rpm rotation of the bit,only a 150 rpm rotor rotation would be required. The decreased torquepenalty can be offset by providing additional (longer) motor stages forexample.

In another embodiment, as shown in FIG. 4, the nutation of the rotor canbe used to drive (or be driven by) the planet carrier of a planetarygearbox at the rotor nutation speed. The rotation of the planet carrierwith respect to the sun gear (or output/input shaft) via the planets andthe relationship of the planet and sun teeth, can dictate the outputshaft rotation as a fixed proportion of the nutation speed. In theembodiment of FIG. 4, the nutation disc of FIG. 3 is replaced by aplanetary gear arrangement which comprises a non-rotating housing 60having the ring gear 62 fixed thereto. The sun gear 64 is fixed to theshaft 48. The end of the rotor shaft 40 connects to a planet gear 66mounted on a planet carrier 68 (further idler planet gears (not shown)may also be mounted on the carrier 68). In this case, the shaft 48rotates in the same direction as the rotor shaft 40 rotates (due to thereversing effect of the gears), but at a rate fω_(N) that is a functionof the nutation dependent on the gear ratios in the planetary gearsystem.

In the embodiments of both FIG. 3 and FIG. 4, the shaft rotation iscoaxial with the drive axis of the motor/pump.

In another embodiment of the invention, connections are provided at bothends of the rotor of a progressive cavity pump, therefore allowing workto be extracted above and below the pump (without the need to runelectrical wires and drive additional electrical motors, or the need toadd two hydraulic motors). A similar benefit is the use of the upperrotation of the rotor when the lower part is attached to a drivingelectrical motor via a gearbox.

Apart from or in addition to the extraction methods of the nutationspeed from the rotor described above, methods of torque and rotationtransmission that are currently used in other technologies can also beused; such as through a dual universal joint configuration, or through aflexible shaft that can flex to accommodate the full offset of the rotornutation. The flexible shaft is subjected to higher fatigue loads, buthas neither moving nor rubbing parts as the universal joints do.

FIGS. 5 and 6 show embodiments using such techniques for connecting toboth ends of the rotor of a progressive cavity device. In FIG. 5, oneend of the rotor 40 is connected to a load/motor 70 by means of aconnection shaft 72 having universal joints 74 at the shaft andload/motor ends. The other end of the rotor shaft 40 is connected to asecond load/motor 76 by means of a flexible shaft 78. In both cases, theloads/motors 70, 76 are driven/drive at the same rate and directionω_(R) as the rotor 40. In FIG. 6, the load/motor 70 is connected to therotor 40 by means of a non-nutating connection 80 of the type describedabove in relation to FIG. 3. The load/motor 76 is connected to the rotor40 by means of a dual universal joint connection 82 of the typedescribed above in relation to FIG. 5. In this case, the load/motor 70operates at the nutation rate, i.e. in the opposite direction to therotor shaft rotation and at a rate ω_(N), whereas the load/motor 76operates at the same rate and direction ω_(R) as the rotor 40.

There are a number of ways in which the embodiments of the invention canbe implemented to involve fluid flow turning the rotor and in turn adrill bit below, but with the added benefit of a rotation above themotor that can be used for grinding or for reaming for example. For apump, an electrical motor below can create the rotor rotation, and therotation above the pump can be used to drive a fluid/air mixer to easedual phase reservoir fluid lift.

The ability to drive the rotor from either end and to extract rotatingmotion from the other (at rotation or nutation speeds) allows for amultitude of applications. Such applications include:

-   -   for drilling applications: using a hydraulic motor to drive a        drill bit at a lower end, and using upper end rotation/nutation        to drive a crusher to protect the stator elastomer by reducing        solids size; or using upper end [higher] nutation speed to power        an alternator and create electricity to power sensors and        actuators (such as for a flow bypass), without having to use        power from the power system of an associated MWD tool;    -   for artificial lift applications: using an electric motor below        to drive the artificial lift pump, with a fluid/air mixer above        to facilitate lift; or using an electric motor above to drive        the pump, and a crusher below to break, or detain and grind        larger rocks before they enter the pump;    -   for wireline drilling and lateral construction applications:        using an electric motor to drive a fluid circulation pump, and a        cuttings crusher below to assure that only small particles enter        the pump section; or using an electric motor to drive a        circulation pump, and using upper rotor rotation or nutation to        drive a backreamer;    -   for a wired Coiled Tubing well cleaning application; using an        electric motor to drive a vacuum/suction pump, and using lower        rotor rotation or nutation to mobilize sand or thick muds (to        break the thixotropy).

These are just preferred examples of embodiments of the invention andother changes within the scope of the invention will be apparent.

1. A progressive cavity device comprising a hollow stator having a rotorshaft positioned therein, wherein the rotor shaft is provided withrotating motion drive connections at both ends thereof.
 2. The device asclaimed in claim 1, wherein the drive connections are adapted to drivethe rotor shaft.
 3. The device as claimed in claim 1, wherein the driveconnections are adapted to extract drive from rotation of the rotorshaft.
 4. The device as claimed in claim 1, wherein at least one of thedrive connections operates at a speed that is different to the rotationspeed of the rotor shaft.
 5. The device as claimed in claim 1, whereinthe drive connections couple to the rotation of the shaft.
 6. The deviceas claimed in claim 5, wherein the drive connections comprise a shaftconnecting two universal joints.
 7. The device as claimed in claim 5,wherein the drive connections comprise a flexible shaft.
 8. The deviceas claimed in claim 1, wherein the drive connections couple to thenutation of the rotor shaft.
 9. The device as claimed in claim 8,wherein the drive connections comprise a non-nutating connection thatimposes a nutation speed on the rotor shaft.
 10. The device as claimedin claim 9, wherein the drive connections comprise a disc mounted forrotation on a further shaft, the rotor shaft being connectedeccentrically to the disc.
 11. The device as claimed in claim 8, whereinthe drive connections comprise a planetary gear system, the rotor shaftbeing connected to a planet gear.
 12. The device as claimed in claim 1,configured to act as a motor or as a pump.
 13. The device as claimed inclaim 12, wherein when configured as a motor, the rotor shaft is drivenby pumping fluid through the hollow stator, and a rotating driveconnection is taken from both ends of the hollow stator to power otherdevices.
 14. The device as claimed in claim 13, wherein the drive at oneend is used to rotate a drill bit.
 15. The device as claimed in claim14, wherein the drive at the other end is used to power a crushingdevice or an electricity generating device.
 16. The device as claimed inclaim 12, wherein when configured as a pump, the rotor shaft is drivenby a drive connection from a motor at one end and a rotating driveconnection is taken from the other end of the rotor shaft to power otherdevices.
 17. The device as claimed in claim 16, wherein the otherdevices to be powered via the rotating drive connection comprise fluidair mixers, crushing devices, reaming or drilling devices and fluidmixing/shearing devices.
 18. A method for powering a crushing device ina wellbore, comprising the steps of: positioning a progressive cavitydevice in the wellbore, the progressive cavity device comprising ahollow stator having a rotor shaft positioned therein, wherein the rotorshaft is provided with rotating motion drive connections at both endsthereof; driving the rotor shaft by pumping fluid through the hollowstator; and powering a crushing device by means of a rotating driveconnection taken from both ends of the hollow stator.